1. Field of the Invention
This invention relates to a thermoplastic polymer composition which has good injection moldability and is capable of yielding molded articles having good stiffness and a good impact resistance at low temperatures. The thermoplastic polymer composition of the present invention is moldable into molded articles as having good characteristic properties suitable for internal and external parts of automobiles and various types of industrial parts.
2. Related Art of the Invention
Thermoplastic polymer compositions comprising blended compositions of polypropylene and ethylene/propylene rubbers have been used as a starting material for obtaining molded articles in various fields including the field of internal and external parts of automobiles. This is because such compositions are moldable into articles which have good mechanical strength and impact resistance, and are excellent in economy and recycling efficiency.
However, the conventional thermoplastic polymer compositions comprising polypropylene and ethylene/propylene rubbers have not been yet satisfactory with respect to injection moldability and the balance of stiffness at normal temperatures and an impact resistance at low temperatures of the molded articles obtained therefrom.
For the purpose of imparting flexibility and processability to polyolefin such as polyethylene, polypropylene and the like, it has been disclosed in Japanese Patent Application Laid-open No. 1-168743 to blend, with the polyolefin, hydrogenated copolymers of isoprene and butadiene having a number average molecular weight of 5000 to 150,000. In this Laid-open publication, no mention is made of the ratio in melt viscosity between the hydrogenated block copolymer and the polyolefin at the time of the blending.